ts way through every capillary
till it reaches another blood-vessel that carries it back to the heart. It
leaves the heart charged with carbonic acid and watery vapor. It returns,
if pure air has met it in the lung, with all corruption destroyed, a
dancing particle of life. But to be life, and not slow death, thirty-three
hogsheads of air must pass daily into the lungs, and twenty-eight pounds
of blood journey from heart to lungs and back again three times in each
hour. It rests wholly with ourselves, whether this wonderful tide, ebbing
and flowing with every breath, shall exchange its poisonous and clogging
carbonic acid and watery vapor for life-giving oxygen, or retain it to
weigh down and debilitate every nerve in the body.

With every thought and feeling some actual particles of brain and nerve
are dissolved, and sent floating on this crimson current. With every
motion of a muscle, whether great or small, with every process that can
take place in the body, this ceaseless change of particles is going on.
Wherever oxygen finds admission, its union with carbon to form carbonic
acid, or with hydrogen to form water, produces heat. The waste of the body
is literally burned up by the oxygen; and it is this burning which means
the warmth of a living body, its absence giving the stony cold of the
dead. "Who shall deliver me from the body of this death?" may well be the
literal question for each day of our lives; and "pure air" alone can
secure genuine life. Breathing bad air reduces all the processes of the
body, lessens vitality; and thus, one in poor health will suffer more from
bad air than those who have become thoroughly accustomed to it. If
weakened vitality were the only result, it would not be so serious a
matter; but scrofula is soon fixed upon such constitutions, beginning with
its milder form as in consumption, but ending in the absolute rottenness
of bone and tissue. The invalid may live in the healthiest climate, pass
hours each day in the open air, and yet undo or neutralize much of the
good of this by sleeping in an unventilated room at night. Diseased
joints, horrible affections of the eye or ear or skin, are inevitable. The
greatest living authorities on lung-diseases pronounce deficient
ventilation the chief cause of consumption, and more fatal _than all other
causes put together_; and, even where food and clothing are both
unwholesome, free air has been found able to counteract their effect.

In the count